This invention relates generally to organoclays, and more specifically relates to a process for improving the ease of dispersion of organoclays in organic liquid compositions.
An organoclay is an organophilic cation-modified clay derived from a clay mineral, generally of the smectite group, for example a bentonite, montmorillonite, hectorite, saponite or the like, by replacing the inorganic exchangeable cations, generally alkali or alkaline earth metal cations, which occur in the natural clay mineral, by organic cations, each comprising at least one hydrocarbon radical which has sufficient carbon atoms to render the surface of the cation-exchanged clay hydrophobic.
Organoclays have been found to be very useful as thixotropic agents in organic media such as, for example, lubricating greases, oil-based drilling fluids, paints, varnishes, enamels and printing inks. However, an organoclay is, in general, difficult to disperse in an organic medium to form the uniform gel structure which is required to thicken, or to increase the viscosity of, the organic medium. Various means have accordingly been used to improve the dispersibility of an organoclay in an organic medium, including the use of a polar organic material, such as a low molecular weight alcohol or ketone, as a dispersing aid, and the use of an excess of a specially selected organic cation in the preparation of the organoclay.
In Finlayson et al, U.S. Pat. No. 4,105,578, an organophilic clay gellant having enhanced dispersibility in organic systems is disclosed which comprises the reaction product of a methyl benzyl dialkyl ammonium compound wherein the compound contains 20 to 35% alkyl groups having 16 carbon atoms, and 60 to 75% alkyl groups having 18 carbon atoms, and a smectite-type clay having a cation exchange capacity of at least 75 milliequivalents per 100 grams of said clay, and wherein the amount of said ammonium compound is from 100 to 120 milliequivalents per 100 grams of said clay, 100% active clay basis.
In Finlayson et al, U.S. Pat. No. 4,412,018, an organophilic clay gellant and methods of using and making same are disclosed, which comprises the reaction product of an organic cation, an organic anion and a smectite-type clay having a cation exchange capacity of at least 75 milliequivalents per 100 grams of said clay, such that an organic cation-organic anion complex is intercalated with the smectite-type clay and the cation exchange sites of the smectite-type clay are substituted with the organic cation.
In our co-pending application Ser. No. 727,022, filed Apr. 25, 1985, we have disclosed a method for treating an organoclay in order that it will disperse readily under low shear in an organic medium to form a homogeneous gel structure without the use of an additional polar organic material. According to such invention there is provided a process which comprises mixing an aqueous suspension of a smectite clay with a quaternary ammonium compound capable of rendering the smectite clay organophilic; subjecting the mixture to high shear mixing for a time sufficient to dissipate in the mixture at least 100 KJ of energy per kg. of dry solids in the mixture; and dewatering the product. The dewatered product is preferably then dried and milled.
The high shear mixing utilized in the invention of our said Ser. No. 727,022 application, is preferably effected by passing the suspension through a homogenizer of the type in which the suspension is forced in the form of a thin film edgewise through a thin, hard surfaced gap under pressure of at least 250 pounds per square inch (1.7 MPa) and at high velocity. A suitable homogenizer is described in British Patent Specification No. 987,176 (or in U.S. Pat. Nos. 3,039,703 and 3,162,379). Such a homogenizer is manufactured by the Manton-Gaulin Company. Advantageously the homogenizer is operated at a pressure of at least 1500 pounds per square inch (10.5 MPa). The amount of energy, in KJ per kg. of dry solids, dissipated in the mixture is given by the expression EQU E=(nP.multidot.10.sup.3)/w
where P is the pressure in MPa exerted in the Manton-Gaulin homogenizer, n is the number of passes through the Manton-Gaulin homogenizer, and w is the weight in grams of dry solids in 1 liter of the aqueous mixture.
While the process disclosed in our Ser. No. 727,022 application, accordingly yields highly effective results, the method necessitates use of the aforementioned high shear technology, which requires use of appropriate apparatus and expenditure of relatively large amounts of energy.
Pursuant to the foregoing, it may be regarded as an object of the present invention, to provide a method which while improving the ease of dispersibility of organoclays in organic liquid compositions, avoids the need to provide high shear mixing equipment and the expenditure of the large amounts of energy which are required for the high shear mixing.